(1) Field of the Invention
This invention relates to a substrate treating apparatus and method for treating, with a treating liquid, substrates such as semiconductor wafers, glass substrates for liquid crystal displays or glass substrates for photomasks (hereinafter called simply “substrates”). More particularly, the invention relates to a technique for adjusting the temperature of the treating liquid.
(2) Description of the Related Art
Conventionally, this type of substrate treating apparatus includes an inner tank for storing a treating liquid and immersing substrates therein, an outer tank for collecting the treating liquid overflowing the inner tank, a piping for interconnecting the inner tank and outer tank for mutual communication, a temperature control unit mounted on the piping, and a circulating pump also mounted on the piping. See Japanese Unexamined Patent Publication No. 2002-100605 (page 5 and FIG. 3), for example.
In the apparatus having the above construction, while the circulating pump delivers the treating liquid under pressure, the temperature control unit adjusts the treating liquid to a predetermined temperature for introduction into the inner tank. An electronic thermal unit or a heater is used as the temperature control unit.
The conventional apparatus noted above has the following drawbacks.
In the conventional apparatus, where an electronic thermal unit is used as the temperature control unit, temperature control is impossible for a relatively high temperature range (e.g. 50-180° C.). With a heater, on the other hand, temperature control can be carried out only with low accuracy for a relatively low temperature range (e.g. 20-40° C.). The heater has a further disadvantage that, when a target temperature for temperature control is set low, the control must depends on a temperature fall by natural cooling, and thus a long time is taken to complete the temperature control. In other words, a temperature control covering a large range cannot be performed efficiently, and temperature control accuracy is low also.
In order to solve the above problems, it is conceivable to bifurcate a portion of the piping, and install an electronic thermal unit on one branch pipe and a heater on the other branch pipe. Temperature control may be carried out with either the electronic thermal unit or the heater according to a target temperature. However, such an exclusive use requires switch valves to be mounted upstream and downstream of the branch pipes. This poses a problem of complicating the construction.